The present invention relates to digital video signal recording/reproducing and, more particularly, to digitally recording/reproducing a vertical resolution signal of a video picture as a color signal. Reference is made to copending application Ser. No. (to be assigned), filed Nov. 3, 1995 (attorney docket 450100-3367, which describes related subject matter.
Video signals are transmitted from a transmission source to a television and are reconstructed by the television into a video picture. A video signal is comprised of different types of signals, such as information signals describing how the video picture is arranged and data signals corresponding to the actual video picture. Video signals are transmitted to televisions in a standard format so that a television can identify the different signals and process them into a video picture.
The PAL plus standard is one such format employed particularly in European countries and is becoming more popular in the United States. The success of the PAL plus standard is due in part to the movie-screen shape of a PAL plus video picture shown in FIG. 1A. With a PAL plus television, viewers can watch a movie in the comfort of their own home with all of the enjoyment of watching the video picture on a movie-theater screen.
The ratio between the width and the height of the video picture is known as the aspect ratio. The PAL plus standard has a 16:9 aspect ratio, which means that the width is almost twice as large as the height of the PAL plus video picture. By comparison, the NTSC television screen in FIG. 1B (the PAL plus video picture superimposed) has a significantly larger aspect ratio than the NTSC screen. That is, the NTSC screen is shaped more like a square than the rectangular, PAL plus video picture.
With the digital compression era, video picture standards are being modified to include digital compression. The PAL plus standard is one such modified version which grew out of the earlier PAL standard. The digital compression in the PAL plus standard is a 4 to 3 decimation, and as shown in FIG. 1C, compresses four lines of the video picture into three lines. The resulting compressed video picture can be thought of as having an upper screen portion, a middle main screen portion and a lower invalid screen portion.
Since the invalid screen portions do not carry video picture data, the PAL plus standard uses these portions to transmit information relating to the video picture. Such information includes a vertical resolution signal, known as a helper signal, which is generated by decimating the video picture using a 4 to 1 decimation process. The helper signal is used during decompression to reconstruct the vertical resolution of the PAL plus video picture.
FIG. 2A is a more detailed depiction of the decimated PAL plus video picture with the first field (lines 60 to 274) corresponding to a luminance signal Y component, and the second field (lines 372 to 586) corresponding to a color difference signal C.sub.B,C.sub.R component (FIG. 3). During the transmission of lines 1 to 22, 311 to 335 and 623 to 624, no signals are transmitted and the television executes a vertical blanking operation; whereby the electron scanning beam is turned off and reset to the upper-left corner of the television screen. Similarly, during the transmission of samples 1 to 9 and 712 to 731, the television executes a horizontal blanking operation and the electron scanning beam is reset to the next line. WSS bits which indicate that a helper signal is forthcoming are located at the beginning of the video picture on line 23. A reference signal which is used to decode the helper signal follows the WSS bits on line 23. Then, the helper signal is transmitted during lines 24 to 59, which correspond to the upper invalid screen portion. The main screen portion is transmitted during lines 60 to 274, wherein the data making up the video picture is transmitted. Finally, another portion of the helper signal is transmitted during lines 274 to 310, thus completing transmission of field 1. Field 2 (lines 336 to 623 is transmitted in a similar fashion to field 1.
The PAL plus standard ascribes to a 4:2:2 (Y:C.sub.R :C.sub.B) sampling scheme corresponding to Recommendation 601 of CCIR (International Radio Consultative Committee; now, ITU-RS). In other words, for every four samples, the luminance signal Y is sampled four times and the color difference signals C.sub.B,C.sub.R are each sampled twice. Thus, the luminance samples signal Y are stored in field 1, while the color difference signals are "doubled-up" and stored together in field 2, as shown in FIG. 2A.
While the PAL plus signal is depicted as a picture in FIG. 2A, the PAL plus signal is transmitted as the stream of data depicted in FIG. 4A. Valid lines 23 to 622 are by sync pulses and each line is separated by horizontal sync pulses. The PAL plus signal begins at line 23 and is shown with the WSS signal and the reference of the helper signal; and ends at line 622. The vertical blanking interval begins at line 623 and includes the white 100% reference level, which indicates the value corresponding to a 100% white portion of the video picture. An analog signal corresponding to the video picture transmitted during the main portions of the PAL plus signal is shown in FIG. 4B. Following the video signal, the helper signal is shown as an analog signal. FIG. 4C shows line 23 in more detail with the WSS signal arranged as a series of bits. FIG. 4D shows line 623 in more detail of the PAL plus signal, wherein the white 100% level reference has a maximum value of 235 and a pedestal is set to 16.
As shown in FIG. 2B, another video picture standard is the EDTV-2 video picture which has a similar configuration to the PAL plus video picture shown in FIG. 2A. As shown, the EDTV-2 video picture has two fields with each field having upper and lower invalid portions and a middle valid portion. The upper and lower invalid portions are multiplexed with vertical resolution signals VT and VH and the middle valid portion is multiplexed with a horizontal resolution signal HH. The VT signal is a vertical time high-band component that is lost in the interlace process when a video signal photographed in the double speed non-interlace mode is transmitted by the interlace mode; and the VH signal is a vertical luminance high-band component that is lost when a video signal with an aspect ratio of 16:9 is formed by decimation into the letter box shape. The HH signal is a horizontal luminance high-band component with a band ranging from 4.2 MHz to 6 MHz and is frequency shifted and multiplexed to the Fukinuki hole (an area in the vertical/temporal frequency domain where the color signals are not located) of the main screen portion. Thus, data in the vertical blanking interval and the horizontal blanking interval is omitted while lines 23 to 232 of a field 1 and lines 285 to 524 of a field 2 are encoded.
Similar to the PAL plus system, EDTV-2 also includes reference signals. NRZ signals (B1 to B4) that represent an aspect ratio are disposed on lines 22 and 285. Identification (ID) signals are disposed that represent whether or not signal components of VT, VH, and HH are present (the ID signals are modulated with a color sub-carrier and identify whether the signal components VT, VH, and HH are present depending upon whether the phase of the modulated signals are phase 0 or in phase with the color sub-carrier). Lastly, a 2.04 MHz confirmation signal that identifies the video signal as a signal corresponding to the EDTV-2 standard is disposed.
A problem arises when a resolution compensation signal is digitally recorded by a digital VCR. As shown in FIG. 5, the luminance Y signal has a bandwidth of approximately 5 MHz and a center frequency of about 2.25 MHz. The chrominance signal C, by contrast, has a smaller bandwidth of about one MHz. The helper signal shown in FIG. 5B has the same center frequency as the chrominance signal C, but has a bandwidth which is within the range of the luminance signal Y. When the helper signal in the first field of the PAL plus video signal is processed as a color signal C the helper signal is truncated because the bandwidth of the chrominance signal C (one MHz) is significantly smaller than the helper signal (five MHz). Thus, the helper signal has not been, heretofore, properly processed and stored on digital media.